1. Field of the Invention
The present invention relates to a large-scale integrated circuit, and in particular to a large-scale integrated circuit that utilizes an existing circuit configuration, and is added to a circuit for expanding functions and correcting a malfunction of the existing circuit.
2. Description of the Related Art
Conventionally, it has been an problem to maintain the functions of an existing device while achieving new functions when a new device is designed by expanding the existing device.
For example, in the field of game machines where compatibility is a serious consideration, there are new game machines that have backward compatibility for existing game machines.
For example, in a case with a game machine A, an LSI chip of an existing game machine A is installed in a new game machine A in order for the new game machine A to have backward compatibility for the existing game machine A. Further, in a case with a game machine B, software emulation for an existing game machine B is performed on a new game machine B in order for the new game machine B to have backward compatibility for the existing game machine B. Conventional game machines have added new functions while maintaining their compatibility in such methods.
However, in the game machine A method for mounting a chip of the existing game machine on a system, two chips, that is an old chip for achieving functions of the existing game machine and a new chip for achieving functions of a new game machine, are implemented on a substrate, causing the cost for the overall system to increase. Further, in the game machine B method for emulating the existing game machine in the new game machine, there is a possibility of not achieving 100% backward compatibility, where there may be software that does not run.
Reference 1 discloses a way to change the functions of an LSI by integrating a plurality of functional blocks on one LSI chip, and allowing only specific functional blocks to be effective with an external terminal.
Specifically, the LSI disclosed in the reference configures a plurality of circuit blocks in one gate array, and the LSI sets one of the plurality of blocks in an operational state based on a mode setting signal provided from outside for a mode setting terminal, and connects a circuit block, which is set in the operational state, and an external connecting terminal so that data can be transferred.
For example, an LSI with such a configuration is equipped with a compatible circuit having compatibility with an existing LSI as a first circuit block, and a new circuit added with a new function to the functions of the existing LSI as a second circuit block. The LSI switches these circuits with an external terminal, so that a compatible LSI having compatibility with the existing LSI and a new LSI having no compatibility with the existing LSI can be achieved within one LSI. Herein, the compatible LSI allows only the first circuit block to be operational by the setting of an external terminal. The new LSI allows only the second circuit block to be operational by the setting of an external terminal.    Reference 1: Japanese Laid-Open Publication No. 7-78876